Copyright

Export of software employing encryption from the United States of
America may require a specific license from the United States
Government. It is the responsibility of any person or organization
contemplating export to obtain such a license before exporting.

WITHIN THAT CONSTRAINT, permission to use, copy, modify, and distribute
this software and its documentation for any purpose and without fee is
hereby granted, provided that the above copyright notice appear in all
copies and that both that copyright notice and this permission notice
appear in supporting documentation, and that the name of M.I.T. not be
used in advertising or publicity pertaining to distribution of the
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and not distribute it in such a fashion that it might be confused with
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suitability of this software for any purpose. It is provided “as is”
without express or implied warranty.

Project Athena, Athena, Athena MUSE, Discuss, Hesiod, Kerberos, Moira,
and Zephyr are trademarks of the Massachusetts Institute of Technology
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“Commercial use” means use of a name in a product or other for-profit
manner. It does NOT prevent a commercial firm from referring to the
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recognition of their trademark status should be given).

The following copyright and permission notice applies to the
OpenVision Kerberos Administration system located in
kadmin/create, kadmin/dbutil, kadmin/passwd,
kadmin/server, lib/kadm5, and portions of
lib/rpc:

Copyright, OpenVision Technologies, Inc., 1996, All Rights Reserved

WARNING: Retrieving the OpenVision Kerberos Administration system source
code, as described below, indicates your acceptance of the following
terms. If you do not agree to the following terms, do not retrieve the
OpenVision Kerberos administration system.

You may freely use and distribute the Source Code and Object Code
compiled from it, with or without modification, but this Source Code is
provided to you “AS IS” EXCLUSIVE OF ANY WARRANTY, INCLUDING, WITHOUT
LIMITATION, ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE, OR ANY OTHER WARRANTY, WHETHER EXPRESS OR IMPLIED.
IN NO EVENT WILL OPENVISION HAVE ANY LIABILITY FOR ANY LOST PROFITS,
LOSS OF DATA OR COSTS OF PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, OR
FOR ANY SPECIAL, INDIRECT, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THIS
AGREEMENT, INCLUDING, WITHOUT LIMITATION, THOSE RESULTING FROM THE USE
OF THE SOURCE CODE, OR THE FAILURE OF THE SOURCE CODE TO PERFORM, OR FOR
ANY OTHER REASON.

OpenVision retains all copyrights in the donated Source Code. OpenVision
also retains copyright to derivative works of the Source Code, whether
created by OpenVision or by a third party. The OpenVision copyright
notice must be preserved if derivative works are made based on the
donated Source Code.

OpenVision Technologies, Inc. has donated this Kerberos Administration
system to MIT for inclusion in the standard Kerberos 5 distribution.
This donation underscores our commitment to continuing Kerberos
technology development and our gratitude for the valuable work which has
been performed by MIT and the Kerberos community.

Portions contributed by Matt Crawford <crawdad@fnal.gov> were work
performed at Fermi National Accelerator Laboratory, which is operated
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DE-AC02-76CHO3000 with the U.S. Department of Energy.

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Copyright 2000 by Zero-Knowledge Systems, Inc.

Permission to use, copy, modify, distribute, and sell this software
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1 Introduction

1.1 What is Kerberos and How Does it Work?

Kerberos V5 is based on the Kerberos authentication system developed
at MIT. Under Kerberos, a client (generally either a user or a service)
sends a request for a ticket to the Key Distribution Center (KDC). The
KDC creates a ticket-granting ticket (TGT) for the client,
encrypts it using the client's password as the key, and sends the
encrypted TGT back to the client. The client then attempts to decrypt
the TGT, using its password. If the client successfully decrypts the
TGT (i.e., if the client gave the correct password), it keeps the
decrypted TGT, which indicates proof of the client's identity.

The TGT, which expires at a specified time, permits the client to obtain
additional tickets, which give permission for specific services. The
requesting and granting of these additional tickets is user-transparent.

1.2 Why Should I use Kerberos?

Since Kerberos negotiates authenticated, and optionally encrypted,
communications between two points anywhere on the Internet, it provides
a layer of security that is not dependent on which side of a firewall
either client is on. Since studies have shown that half of the computer
security breaches in industry happen from inside firewalls,
Kerberos V5 from MIT will play a vital role in the
security of your network.

1.3 Please Read the Documentation

As with any software package that uses a centrallized database, the
installation procedure is somewhat involved, and requires forethought
and planning. MIT has attempted to make this
Kerberos V5 Installation Guide as concise as possible, rather than
making it an exhaustive description of the details of Kerberos.
Consequently, everything in this guide appears because MIT
believes that it is important. Please read and follow these
instructions carefully.

This document is one piece of the document set for Kerberos V5. The
documents, and their intended audiences, are:

Kerberos V5 Installation Guide: a concise guide for installing
Kerberos V5. Kerberos administrators (particularly whoever will be
making site-wide decisions about the installation) and the system
administrators who will be installing the software should read this
guide.

Kerberos V5 System Administrator's Guide: a sysadmin's guide to
administering a Kerberos installation. The System Administrator's Guide
describes the administration software and suggests policies and
procedures for administering a Kerberos installation. Anyone who will
have administrative access to your Kerberos database should read this
guide.

Kerberos V5 UNIX User's Guide: a guide to using the Kerberos
UNIX client programs. All users on UNIX systems should read this guide,
particularly the “Tutorial” section.

2.1 Kerberos Realms

Although your Kerberos realm can be any ASCII string, convention is to
make it the same as your domain name, in upper-case letters. For
example, hosts in the domain example.com would be in the
Kerberos realm EXAMPLE.COM.

If you need multiple Kerberos realms, MIT recommends that
you use descriptive names which end with your domain name, such as
BOSTON.EXAMPLE.COM and HOUSTON.EXAMPLE.COM.

2.2 Mapping Hostnames onto Kerberos Realms

Mapping hostnames onto Kerberos realms is done in one of two ways.

The first mechanism, which has been in use for years in MIT-based
Kerberos distributions, works through a set of rules in
the krb5.conf configuration file. (See krb5.conf.) You can
specify mappings for an entire domain or subdomain, and/or on a
hostname-by-hostname basis. Since greater specificity takes precedence,
you would do this by specifying the mappings for a given domain or
subdomain and listing the exceptions.

The second mechanism works by looking up the information in special
TXT records in the Domain Name Service. This is currently not
used by default because security holes could result if the DNS TXT
records were spoofed. If this mechanism is enabled on the client,
it will try to look up a TXT record for the DNS name formed by
putting the prefix _kerberos in front of the hostname in question.
If that record is not found, it will try using _kerberos and the
host's domain name, then its parent domain, and so forth. So for the
hostname BOSTON.ENGINEERING.FOOBAR.COM, the names looked up would be:

The value of the first TXT record found is taken as the realm name.
(Obviously, this doesn't work all that well if a host and a subdomain
have the same name, and different realms. For example, if all the hosts
in the ENGINEERING.FOOBAR.COM domain are in the ENGINEERING.FOOBAR.COM
realm, but a host named ENGINEERING.FOOBAR.COM is for some reason in
another realm. In that case, you would set up TXT records for all
hosts, rather than relying on the fallback to the domain name.)

Even if you do not choose to use this mechanism within your site, you
may wish to set it up anyway, for use when interacting with other sites.

2.3 Ports for the KDC and Admin Services

The default ports used by Kerberos are port 88 for the
KDC1 and
port 749 for the admin server. You can, however,
choose to run on other ports, as long as they are specified in each
host's /etc/services and krb5.conf files, and the
kdc.conf file on each KDC. For a more thorough treatment of
port numbers used by the Kerberos V5 programs, refer to the
“Configuring Your Firewall to Work With Kerberos V5” section of
the Kerberos V5 System Administrator's Guide.

2.4 Slave KDCs

Slave KDCs provide an additional source of Kerberos ticket-granting
services in the event of inaccessibility of the master KDC. The number
of slave KDCs you need and the decision of where to place them, both
physically and logically, depends on the specifics of your network.

All of the Kerberos authentication on your network requires that each
client be able to contact a KDC. Therefore, you need to anticipate any
likely reason a KDC might be unavailable and have a slave KDC to take up
the slack.

Some considerations include:

Have at least one slave KDC as a backup, for when the master KDC is
down, is being upgraded, or is otherwise unavailable.

If your network is split such that a network outage is likely to cause a
network partition (some segment or segments of the network to become cut
off or isolated from other segments), have a slave KDC accessible to
each segment.

If possible, have at least one slave KDC in a different building from
the master, in case of power outages, fires, or other localized
disasters.

2.5 Hostnames for the Master and Slave KDCs

MIT recommends that your KDCs have a predefined set of
CNAME records (DNS hostname aliases), such as kerberos
for the master KDC and
kerberos-1, kerberos-2, ... for the
slave KDCs. This way, if you need to swap a machine, you only need to
change a DNS entry, rather than having to change hostnames.

A new mechanism for locating KDCs of a realm through DNS has been added
to the MIT Kerberos V5 distribution. A relatively new
record type called SRV has been added to DNS. Looked up by a
service name and a domain name, these records indicate the hostname and
port number to contact for that service, optionally with weighting and
prioritization. (See RFC 2782 if you want more information. You can
follow the example below for straightforward cases.)

The use with Kerberos is fairly straightforward. The domain name used
in the SRV record name is the domain-style Kerberos realm name. (It is
possible to have Kerberos realm names that are not DNS-style names, but
we don't recommend it for Internet use, and our code does not support it
well.) Several different Kerberos-related service names are used:

_kerberos._udp

This is for contacting any KDC by UDP. This entry will be used the most
often. Normally you should list port 88 on each of your KDCs.

_kerberos._tcp

This is for contacting any KDC by TCP. The MIT KDC by default will not
listen on any TCP ports, so unless you've changed the configuration or
you're running another KDC implementation, you should leave this
unspecified. If you do enable TCP support, normally you should use
port 88.

_kerberos-master._udp

This entry should refer to those KDCs, if any, that will immediately see
password changes to the Kerberos database. This entry is used only in
one case, when the user is logging in and the password appears to be
incorrect; the master KDC is then contacted, and the same password used
to try to decrypt the response, in case the user's password had recently
been changed and the first KDC contacted hadn't been updated. Only if
that fails is an “incorrect password” error given.

If you have only one KDC, or for whatever reason there is no accessible
KDC that would get database changes faster than the others, you do not
need to define this entry.

_kerberos-adm._tcp

This should list port 749 on your master KDC.
Support for it is not complete at this time, but it will eventually be
used by the kadmin program and related utilities. For now, you
will also need the admin_server entry in krb5.conf.
(See krb5.conf.)

_kpasswd._udp

This should list port 464 on your master KDC.
It is used when a user changes her password.

_kerberos-iv._udp

This should refer to your KDCs that serve Kerberos version 4 requests,
if you have Kerberos v4 enabled.

Be aware, however, that the DNS SRV specification requires that the
hostnames listed be the canonical names, not aliases. So, for example,
you might include the following records in your (BIND-style) zone file:

As with the DNS-based mechanism for determining the Kerberos realm of a
host, we recommend distributing the information this way for use by
other sites that may want to interact with yours using Kerberos, even if
you don't immediately make use of it within your own site. If you
anticipate installing a very large number of machines on which it will
be hard to update the Kerberos configuration files, you may wish to do
all of your Kerberos service lookups via DNS and not put the information
(except for admin_server as noted above) in future versions of
your krb5.conf files at all. Eventually, we hope to phase out
the listing of server hostnames in the client-side configuration files;
making preparations now will make the transition easier in the future.

2.6 Database Propagation

The Kerberos database resides on the master KDC, and must be propagated
regularly (usually by a cron job) to the slave KDCs. In deciding how
frequently the propagation should happen, you will need to balance the
amount of time the propagation takes against the maximum reasonable
amount of time a user should have to wait for a password change to take
effect.

If the propagation time is longer than this maximum reasonable time
(e.g., you have a particularly large database, you have a lot of
slaves, or you experience frequent network delays), you may wish to
cut down on your propagation delay by performing the propagation in
parallel. To do this, have the master KDC propagate the database to one
set of slaves, and then have each of these slaves propagate the database
to additional slaves.

3 Building Kerberos V5

Kerberos V5 uses a configuration system built using the Free
Software Foundation's autoconf program. This system makes
Kerberos V5 much simpler to build and reduces the amount of effort
required in porting Kerberos V5 to a new platform.

3.1.1 The appl Directory

The Kerberos release provides certain UNIX utilities, modified to use
Kerberos authentication. In the appl/bsd directory are the
Berkeley utilities login, rlogin, rsh, and rcp, as well as
the associated daemons kshd and klogind. The login program
obtains ticket-granting tickets for users upon login; the other utilities
provide authenticated Unix network services.

The appl directory also contains Kerberized telnet and ftp programs,
as well as sample Kerberos application client and server programs.

3.1.3 The gen-manpages Directory

There are two manual pages in this directory. One is an introduction
to the Kerberos system. The other describes the .k5login file
which allows users to give access with their UID to other users
authenticated by the Kerberos system.

3.1.4 The include Directory

3.1.5 The kadmin Directory

In this directory is the code for the utilities kadmin,
kadmin.local, kdb5_util, and ktutil.
ktutil is the Kerberos keytab file maintenance utility from
which a Kerberos administrator can read, write, or edit entries in a
Kerberos V5 keytab or Kerberos V4 srvtab. kadmin and
kadmin.local are command-line interfaces to the Kerberos V5 KADM5
administration system. kadmin.local runs on the master KDC and
does not use Kerberos to authenticate to the database, while
kadmin uses Kerberos authentication and an encrypted RPC. The
two provide identical functionalities, which allow administrators to
modify the database of Kerberos principals. kdb5_util allows
administrators to perform low-level maintenance procedures on Kerberos
and the KADM5 database. With this utility, databases can be created,
destroyed, or dumped to and loaded from ASCII files. It can also be
used to create master key stash files.

3.1.7 The krb524 Directory

This directory contains the code for krb524, a service that
converts Kerberos V5 credentials into Kerberos V4 credentials suitable
for use with applications that for whatever reason do not use V5
directly.

3.1.8 The lib Directory

The lib directory contain 10 subdirectories as well as some
definition and glue files. The crypto subdirectory contains the
Kerberos V5 encryption library. The des425 subdirectory exports
the Kerberos V4 encryption API, and translates these functions into
calls to the Kerberos V5 encryption API. The gssapi library
contains the Generic Security Services API, which is a library of
commands to be used in secure client-server communication. The
kadm5 directory contains the libraries for the KADM5 administration
utilities. The Kerberos 5 database libraries are contained in
kdb. The directories krb4 and krb5 contain the Kerberos 4
and Kerberos 5 APIs, respectively. The rpc directory contains the
API for the Kerberos Remote Procedure Call protocol.

3.1.9 The prototype Directory

This directory contains several template files. The prototype.h
and prototype.c files contain the MIT copyright message and a
placeholder for the title and description of the file.
prototype.h also has a short template for writing ifdef
and ifndef preprocessor statements. The getopt.c file
provides a template for writing code that will parse the options with
which a program was called.

3.1.10 The slave Directory

This directory contains code which allows for the propagation of the
Kerberos principal database from the master KDC to slave KDCs over an
encrypted, secure channel. kprop is the program which actually
propagates the database dump file. kpropd is the Kerberos V5
slave KDC update server which accepts connections from the kprop
program. kslave_update is a script that takes the name of a
slave server, and propagates the database to that server if the
database has been modified since the last dump or if the database has
been dumped since the last propagation.

3.1.11 The util Directory

This directory contains several utility programs and libraries. The
programs used to configure and build the code, such as autoconf,
lndir, kbuild, reconf, and makedepend,
are in this directory. The profile directory contains most of the
functions which parse the Kerberos configuration files (krb5.conf
and kdc.conf). Also in this directory are the Kerberos error table
library and utilities (et), the Sub-system library and utilities
(ss), database utilities (db2), pseudo-terminal utilities
(pty), bug-reporting program send-pr, and a generic
support library support used by several of our other libraries.

3.2 Build Requirements

In order to build Kerberos V5, you will need approximately 60-70
megabytes of disk space. The exact amount will vary depending on the
platform and whether the distribution is compiled with debugging symbol
tables or not.

If you wish to keep a separate build tree, which contains the compiled
*.o file and executables, separate from your source tree, you
will need a make program which supports VPATH, or
you will need to use a tool such as lndir to produce a symbolic
link tree for your build tree.

3.3 Unpacking the Sources

The first step in each of these build procedures is to unpack the
source distribution. The Kerberos V5 distribution comes in a tar file,
generally named krb5-1.6.tar, which contains a
compressed tar file consisting of the sources for all of Kerberos
(generally krb5-1.6.tar.gz) and a PGP signature for
this source tree (generally krb5-1.6.tar.gz.asc).
MIT highly recommends that you verify the integrity of the
source code using this signature.

Unpack the compressed tar file in some directory, such as
/u1/krb5-1.6. (In the rest of this document, we
will assume that you have chosen to unpack the Kerberos V5 source
distribution in this directory. Note that the tarfiles will by default
all unpack into the ./krb5-1.6 directory, so that if
your current directory is /u1 when you unpack the tarfiles, you
will get /u1/krb5-1.6/src, etc.)

3.4 Doing the Build

You have a number of different options in how to build Kerberos. If you
only need to build Kerberos for one platform, using a single directory
tree which contains both the source files and the object files is the
simplest. However, if you need to maintain Kerberos for a large number
of platforms, you will probably want to use separate build trees for
each platform. We recommend that you look at OS Incompatibilities, for notes that we have on particular operating
systems.

3.4.2 Building with Separate Build Directories

If you wish to keep separate build directories for each platform, you
can do so using the following procedure. (Note, this requires that your
make program support VPATH. GNU's make will provide this
functionality, for example.) If your make program does not
support this, see the next section.

For example, if you wish to create a build directory for pmax binaries
you might use the following procedure:

3.4.3 Building Using lndir

If you wish to keep separate build directories for each platform, and
you do not have access to a make program which supports VPATH,
all is not lost. You can use the lndir program to create
symbolic link trees in your build directory.

For example, if you wish to create a build directory for solaris binaries
you might use the following procedure:

mkdir /u1/krb5-1.6/solaris

cd /u1/krb5-1.6/solaris

/u1/krb5-1.6/src/util/lndir `pwd`/../src

./configure

make

You must give an absolute pathname to lndir because it has a bug that
makes it fail for relative pathnames. Note that this version differs
from the latest version as distributed and installed by the XConsortium
with X11R6. Either version should be acceptable.

3.5 Installing the Binaries

Once you have built Kerberos, you should install the binaries. You
can do this by running:

% make install

If you want to install the binaries into a destination directory that
is not their final destination, which may be convenient if you want to
build a binary distribution to be deployed on multiple hosts, you may
use:

% make install DESTDIR=/path/to/destdir

This will install the binaries under DESTDIR/PREFIX, e.g., the
user programs will install into DESTDIR/PREFIX/bin, the
libraries into DESTDIR/PREFIX/lib, etc.

Note that if you want to test the build (see Testing the Build),
you usually do not need to do a make install first.

Some implementations of make allow multiple commands to be run in
parallel, for faster builds. We test our Makefiles in parallel builds with
GNU make only; they may not be compatible with other parallel build
implementations.

3.6 Testing the Build

The Kerberos V5 distribution comes with built-in regression tests. To
run them, simply type the following command while in the top-level build
directory (i.e., the directory where you sent typed make to start
building Kerberos; see Doing the Build.):

% make check

However, there are several prerequisites that must be satisfied first:

Configure and build Kerberos with Tcl support. Tcl is used to drive the
test suite. This often means passing --with-tcl to configure to
tell it the location of the Tcl configuration script. (See
See Options to Configure.)

You have to run make install before running make check, or
the test suite will often pick up the installed version of Kerberos
rather than the newly built one. You can install into a prefix that
isn't in the system library search path, though. This theoretically
could be fixed with the appropriate environment variable magic in the
test suite, but hasn't been yet.

In order to test the RPC layer, the local system has to be running the
portmap daemon and it has to be listening to the regular
network interface (not just localhost).

3.6.1 The DejaGnu Tests

Some of the built-in regression tests are setup to use the DejaGnu
framework for running tests. These tests tend to be more comprehensive
than the normal built-in tests as they setup test servers and test
client/server activities.

DejaGnu may be found wherever GNU software is archived.

Most of the tests are setup to run as a non-privileged user. For some
of the krb-root tests to work properly, either (a) the user running the
tests must not have a .k5login file in the home directory or (b) the
.k5login file must contain an entry for <username>@KRBTEST.COM.
There are two series of tests (rlogind and telnetd) which
require the ability to rlogin as root to the local
machine. Admittedly, this does require the use of a .rhosts file
or some authenticated means. 2

If you cannot obtain root access to your machine, all the other tests
will still run. Note however, with DejaGnu 1.2, the "untested testcases"
will cause the testsuite to exit with a non-zero exit status which
make will consider a failure of the testing process. Do not worry
about this, as these tests are the last run when make check is
executed from the top level of the build tree. This problem does not
exist with DejaGnu 1.3.

3.6.2 The KADM5 Tests

Regression tests for the KADM5 system, including the GSS-RPC, KADM5
client and server libraries, and kpasswd, are also included in this
release. Each set of KADM5 tests is contained in a sub-directory called
unit-test directly below the system being tested. For example,
lib/rpc/unit-test contains the tests for GSS-RPC. The tests are all
based on DejaGnu (but they are not actually called part of "The DejaGnu
tests," whose naming predates the inclusion of the KADM5 system). In
addition, they require the Tool Command Language (TCL) header files and
libraries to be available during compilation and some of the tests also
require Perl in order to operate. If all of these resources are not
available during configuration, the KADM5 tests will not run. The TCL
installation directory can be specified with the --with-tcl
configure option. (See See Options to Configure.) The runtest and
perl programs must be in the current execution path.

If you install DejaGnu, TCL, or Perl after configuring and building
Kerberos and then want to run the KADM5 tests, you will need to
re-configure the tree and run make at the top level again to make
sure all the proper programs are built. To save time, you actually only
need to reconfigure and build in the directories src/kadmin/testing,
src/lib/rpc, src/lib/kadm5.

3.7 Options to Configure

There are a number of options to configure which you can use to
control how the Kerberos distribution is built. The following table
lists the most commonly used options to Kerberos V5's configure
program.

--help

Provides help to configure. This will list the set of commonly used
options for building Kerberos.

--prefix=PREFIX

By default, Kerberos will install the package's files rooted at
`/usr/local' as in `/usr/local/bin', `/usr/local/sbin', etc. If you
desire a different location, use this option.

--exec-prefix=EXECPREFIX

This option allows one to separate the architecture independent programs
from the configuration files and manual pages.

--localstatedir=LOCALSTATEDIR

This option sets the directory for locally modifiable single-machine
data. In Kerberos, this mostly is useful for setting a location for the
KDC data files, as they will be installed in
LOCALSTATEDIR/krb5kdc, which is by default
PREFIX/var/krb5kdc.

CC=COMPILER

Use COMPILER as the C compiler.

CFLAGS=FLAGS

Use FLAGS as the default set of C compiler flags.

Note that if you use the native Ultrix compiler on a
DECstation you are likely to lose if you pass no flags to cc; md4.c
takes an estimated 3,469 billion years to compile if you provide neither
the -g flag nor the -O flag to cc.

CPPFLAGS=CPPOPTS

Use CPPOPTS as the default set of C preprocessor flags. The most
common use of this option is to select certain #define's for use
with the operating system's include files.

LD=LINKER

Use LINKER as the default loader if it should be different from C
compiler as specified above.

LDFLAGS=LDOPTS

This option allows one to specify optional arguments to be passed to the
linker. This might be used to specify optional library paths.

This option enables Kerberos V4 backwards compatibility using a
pre-existing Kerberos V4 installation. The directory specified by
KRB4DIR specifies where the V4 header files should be found
(KRB4DIR/include) as well as where the V4 Kerberos library should
be found (KRB4DIR/lib).

--without-krb4

Disables Kerberos V4 backwards compatibility. This prevents Kerberos V4
clients from using the V5 services including the KDC. This would be
useful if you know you will never install or need to interact with V4
clients.

--with-netlib[=libs]

Allows for suppression of or replacement of network libraries. By
default, Kerberos V5 configuration will look for -lnsl and
-lsocket. If your operating system has a broken resolver library
(see Solaris versions 2.0 through 2.3) or fails to pass the tests in
src/tests/resolv you will need to use this option.

--with-tcl=TCLPATH

Some of the unit-tests in the build tree rely upon using a program in
Tcl. The directory specified by TCLPATH specifies where the Tcl
header file (TCLPATH/include/tcl.h as well as where the Tcl
library should be found (TCLPATH/lib).

--enable-shared

This option will turn on the building and use of shared library objects
in the Kerberos build. This option is only supported on certain
platforms.

--enable-dns

--enable-dns-for-kdc

--enable-dns-for-realm

Enable the use of DNS to look up a host's Kerberos realm, or a realm's
KDCs, if the information is not provided in krb5.conf. See Hostnames for the Master and Slave KDCs for information about using DNS to
locate the KDCs, and Mapping Hostnames onto Kerberos Realms for
information about using DNS to determine the default realm. By default,
DNS lookups are enabled for the former but not for the latter.

--enable-kdc-replay-cache

Enable a cache in the KDC to detect retransmitted messages, and resend
the previous responses to them. This protects against certain types of
attempts to extract information from the KDC through some of the
hardware preauthentication systems.

--with-system-et

Use an installed version of the error-table support software, the
compile_et program, the com_err.h header file and the
com_err library. If these are not in the default locations,
you may wish to specify CPPFLAGS=-I/some/dir and
LDFLAGS=-L/some/other/dir options at configuration time as
well.

If this option is not given, a version supplied with the Kerberos
sources will be built and installed along with the rest of the
Kerberos tree, for Kerberos applications to link against.

--with-system-ss

Use an installed version of the subsystem command-line interface
software, the mk_cmds program, the ss/ss.h header file
and the ss library. If these are not in the default locations,
you may wish to specify CPPFLAGS=-I/some/dir and
LDFLAGS=-L/some/other/dir options at configuration time as
well. See also the SS_LIB option.

If this option is not given, the ss library supplied with the
Kerberos sources will be compiled and linked into those programs that
need it; it will not be installed separately.

SS_LIB=libs...

If -lss is not the correct way to link in your installed
ss library, for example if additional support libraries are
needed, specify the correct link options here. Some variants of this
library are around which allow for Emacs-like line editing, but
different versions require different support libraries to be
explicitly specified.

This option is ignored if --with-system-ss is not specified.

--with-system-db

Use an installed version of the Berkeley DB package, which must
provide an API compatible with version 1.85. This option is
unsupported and untested. In particular, we do not know if the
database-rename code used in the dumpfile load operation will behave
properly.

If this option is not given, a version supplied with the Kerberos
sources will be built and installed. (We are not updating this
version at this time because of licensing issues with newer versions
that we haven't investigated sufficiently yet.)

DB_HEADER=headername.h

If db.h is not the correct header file to include to compile
against the Berkeley DB 1.85 API, specify the correct header file name
with this option. For example, DB_HEADER=db3/db_185.h.

DB_LIB=libs...

If -ldb is not the correct library specification for the
Berkeley DB library version to be used, override it with this option.
For example, DB_LIB=-ldb-3.3.

For example, in order to configure Kerberos on a Solaris machine using
the suncc compiler with the optimizer turned on, run the configure
script with the following options:

% ./configure CC=suncc CFLAGS=-O

For a slightly more complicated example, consider a system where
several packages to be used by Kerberos are installed in
/usr/foobar, including Berkeley DB 3.3, and an ss
library that needs to link against the curses library. The
configuration of Kerberos might be done thus:

3.8 osconf.h

There is one configuration file which you may wish to edit to control
various compile-time parameters in the Kerberos distribution:
include/stock/osconf.h. The list that follows is by no means
complete, just some of the more interesting variables.

Please note: The former configuration file config.h no longer
exists as its functionality has been merged into the auto-configuration
process. See Options to Configure.

DEFAULT_PROFILE_PATH

The pathname to the file which contains the profiles for the known realms,
their KDCs, etc. The default value is /etc/krb5.conf.

The profile file format is no longer the same format as Kerberos V4's
krb.conf file.

DEFAULT_KEYTAB_NAME

The type and pathname to the default server keytab file (the
equivalent of Kerberos V4's /etc/srvtab). The default is
/etc/krb5.keytab.

DEFAULT_KDC_ENCTYPE

The default encryption type for the KDC. The default value is
des3-cbc-sha1.

KDCRCACHE

The name of the replay cache used by the KDC. The default value is
krb5kdc_rcache.

RCTMPDIR

The directory which stores replay caches. The default is to try
/var/tmp, /usr/tmp, /var/usr/tmp, and /tmp.

DEFAULT_KDB_FILE

The location of the default database. The default value is
/usr/local/var/krb5kdc/principal.

3.9 Shared Library Support

Shared library support is provided for a few operating systems. There
are restrictions as to which compiler to use when using shared
libraries. In all cases, executables linked with the shared libraries in
this build process will have built in the location of the libraries,
therefore obliterating the need for special LD_LIBRARY_PATH, et al environment
variables when using the programs. Except where noted, multiple versions
of the libraries may be installed on the same system and continue to
work.

Shared library support has been tested on the following platforms but
not exhaustively (they have been built but not necessarily tested in an
installed state): Tru64 (aka Alpha OSF/1 or Digital Unix) 4.0, and
HP/UX 10.20.

Platforms for which there is shared library support but not significant
testing include FreeBSD, OpenBSD, AIX (4.3.3), Linux, NetBSD 1.4.x
(i386), and SunOS 4.x.

To enable shared libraries on the above platforms, run the configure
script with the option --enable-shared.

3.10 Operating System Incompatibilities

This section details operating system incompatibilities with Kerberos V5
which have been reported to the developers at MIT. If you find
additional incompatibilities, and/or discover workarounds to such
problems, please send a report via the krb5-send-pr program.
Thanks!

3.10.3 Alpha OSF/1 V2.0

There used to be a bug when using the native compiler in compiling
md4.c when compiled without either the -O or -g
compiler options. We have changed the code and there is no problem
under V2.1, but we do not have access to V2.0 to test and see if the
problem would exist there. (We welcome feedback on this issue). There
was never a problem in using GCC version 2.6.3.

In version 3.2 and beyond of the operating system, we have not seen
this sort of problem with the native compiler.

3.10.4 Alpha OSF/1 (Digital UNIX) V4.0

The C compiler provided with Alpha OSF/1 V4.0 (a.k.a. Digital UNIX)
defaults to an extended K&R C mode, not ANSI C. You need to provide
the -std argument to the compiler (i.e., ./configure
CC='cc -std') to enable extended ANSI C mode. More recent versions
of the operating system, such as 5.0, seem to have C compilers which
default to -std.

3.10.5 BSDI

BSDI versions 1.0 and 1.1 reportedly has a bad sed which causes
it to go into an infinite loop during the build. The work around is
to use a sed from somewhere else, such as GNU. (This may be
true for some versions of other systems derived from BSD 4.4, such as
NetBSD and FreeBSD.)

3.10.6 HPUX

The native (bundled) compiler for HPUX currently will not work,
because it is not a full ANSI C compiler. The optional ANSI C
compiler should work as long as you give it the -Ae flag
(i.e. ./configure CC='cc -Ae'). This is equivalent to
./configure CC='c89 -D_HPUX_SOURCE', which was the previous
recommendation. This has only been tested recently for HPUX 10.20.

You will need to configure with --disable-shared
--enable-static, because as of 1.4 we don't have support for HPUX
shared library finalization routines, nor the option (yet) to ignore
that lack of support (which means repeated
dlopen/dlclose cycles on the Kerberos libraries may not
be safe) and build the shared libraries anyways.

You will also need to configure the build tree with
--disable-thread-support if you are on HPUX 10 and do not have
the DCE development package installed, because that's where the
pthread.h header file is found. (We don't know if our code
will work with such a package installed, because according to some HP
documentation, their pthread.h has to be included before any
other header files, and our code doesn't do that.)

If you use GCC, it may work, but some versions of GCC have omitted
certain important preprocessor defines, like __STDC_EXT__ and
__hpux.

3.10.7 Solaris versions 2.0 through 2.3

The gethostbyname() routine is broken; it does not return a fully
qualified domain name, even if you are using the Domain Name Service
routines. Since Kerberos V5 uses the fully qualified domain name as the
second component of a service principal (i.e,
host/tsx-11.mit.edu@ATHENA.MIT.EDU), this causes problems for servers
who try to figure out their own fully qualified domain name.

Workarounds:

Supply your own resolver library. (such as bind-4.9.3pl1 available
from ftp.vix.com)

Upgrade to Solaris 2.4

Make sure your /etc/nsswitch.conf has `files' before `dns' like:

hosts: files dns

and then in /etc/hosts, make sure there is a line with your
workstation's IP address and hostname, with the fully qualified domain
name first. Example:

18.172.1.4 dcl.mit.edu dcl

Note that making this change may cause other programs in your
environment to break or behave differently.

3.10.8 Solaris 2.X

You must compile Kerberos V5 without the UCB compatibility
libraries. This means that /usr/ucblib must not be in the
LD_LIBRARY_PATH environment variable when you compile it. Alternatively
you can use the -i option to cc, by using the specifying
CFLAGS=-i option to configure.

If you are compiling for a 64-bit execution environment, you may need
to configure with the option CFLAGS="-D_XOPEN_SOURCE=500
-D__EXTENSIONS__". This is not well tested; at MIT we work primarily
with the 32-bit execution environment.

3.10.9 Solaris 9

Solaris 9 has a kernel race condition which causes the final output
written to the slave side of a pty to be lost upon the final close()
of the slave device. This causes the dejagnu-based tests to fail
intermittently. A workaround exists, but requires some help from the
scheduler, and the “make check” must be executed from a shell with
elevated priority limits.

Run something like

priocntl -s -c FX -m 30 -p 30 -i pid nnnn

as root, where nnnn is the pid of the shell whose priority
limit you wish to raise.

Sun has released kernel patches for this race condition. Apply patch
117171-11 for sparc, or patch 117172-11 for x86. Later revisions of
the patches should also work. It is not necessary to run “make
check” from a shell with elevated priority limits once the patch has
been applied.

3.10.10 SGI Irix 5.X

If you are building in a tree separate from the source tree, the vendors
version of make does not work properly with regards to
VPATH. It also has problems with standard inference rules in 5.2
(not tested yet in 5.3) so one needs to use GNU's make.

Under 5.2, there is a bug in the optional System V -lsocket
library in which the routine gethostbyname() is broken. The
system supplied version in -lc appears to work though so one may
simply specify --with-netlib option to configure.

In 5.3, gethostbyname() is no longer present in -lsocket and
is no longer an issue.

3.11 Using Autoconf

(If you are not a developer, you can skip this section.)

In most of the Kerberos V5 source directories, there is a
configure script which automatically determines the compilation
environment and creates the proper Makefiles for a particular
platform. These configure files are generated using
autoconf, which can be found in the src/util/autoconf
directory in the distribution.

Normal users will not need to worry about running autoconf; the
distribution comes with the configure files already prebuilt.
Developers who wish to modify the configure.in files should see
Overview (The Autoconf Manual).

Note that in order to run autoconf, you must have GNU m4
in your path. Before you use the autoconf in the Kerberos V5
source tree, you may also need to run configure, and then run
make in the src/util/autoconf directory in order to
properly set up autoconf.

One tool which is provided for the convenience of developers can be
found in src/util/reconf. This program should be run while the
current directory is the top source directory. It will automatically
rebuild any configure files which need rebuilding. If you know
that you have made a change that will require that all the
configure files need to be rebuilt from scratch, specify the
--force option:

% cd /u1/krb5-1.6/src
% ./util/reconf --force

The developmental sources are a raw source tree (before it's been packaged
for public release), without the pre-built configure files.
In order to build from such a source tree, you must do:

% cd krb5/util/autoconf
% ./configure
% make
% cd ../..
% util/reconf

Then follow the instructions for building packaged source trees (above).
To install the binaries into a binary tree, do:

% cd /u1/krb5-1.6/src
% make all
% make install DESTDIR=somewhere-else

4.1 Installing KDCs

The Key Distribution Centers (KDCs) issue Kerberos tickets. Each KDC
contains a copy of the Kerberos database. The master KDC contains the
master copy of the database, which it propagates to the slave KDCs at
regular intervals. All database changes (such as password changes) are
made on the master KDC.

Slave KDCs provide Kerberos ticket-granting services, but not database
administration. This allows clients to continue to obtain tickets when
the master KDC is unavailable.

MIT recommends that you install all of your KDCs to be able
to function as either the master or one of the slaves. This will enable
you to easily switch your master KDC with one of the slaves if
necessary. (See Switching Master and Slave KDCs.) This installation
procedure is based on that recommendation.

4.1.1.1 Edit the Configuration Files

Modify the configuration files, /etc/krb5.conf and
/usr/local/var/krb5kdc/kdc.conf to reflect the correct
information (such as the hostnames and realm name) for your realm.
MIT recommends that you keep krb5.conf in /etc.

Most of the tags in the configuration have default values that will
work well for most sites. There are some tags in the krb5.conf
file whose values must be specified, and this section will explain
those as well as give an overview of all of the sections in both
configuration files. For more information on changing defaults with
the configuration files, see the Kerberos V5 System Administrator's
Guide sections on configuration files.

4.1.1.2 krb5.conf

The krb5.conf file contains Kerberos configuration information,
including the locations of KDCs and admin servers for the Kerberos
realms of interest, defaults for the current realm and for Kerberos
applications, and mappings of hostnames onto Kerberos realms. Normally,
you should install your krb5.conf file in the directory
/etc. You can override the default location by setting the
environment variable KRB5_CONFIG.

The krb5.conf file is set up in the style of a Windows INI file.
Sections are headed by the section name, in square brackets. Each
section may contain zero or more relations, of the form:

foo = bar

or

fubar = {
foo = bar
baz = quux
}

Placing a `*' at the end of a line indicates that this is the
final value for the tag. This means that neither the remainder
of this configuration file nor any other configuration file will be
checked for any other values for this tag.

For example, if you have the following lines:

foo = bar*
foo = baz

then the second value of foo (baz) would never be read.

The krb5.conf file may contain any or all of the following
sections:

libdefaults

Contains default values used by the Kerberos V5 library.

login

Contains default values used by the Kerberos V5 login program.

appdefaults

Contains default values that can be used by Kerberos V5 applications.

realms

Contains subsections keyed by Kerberos realm names. Each subsection
describes realm-specific information, including where to find the
Kerberos servers for that realm.

domain_realm

Contains relations which map domain names and subdomains onto Kerberos
realm names. This is used by programs to determine what realm a host
should be in, given its fully qualified domain name.

logging

Contains relations which determine how Kerberos programs are to perform
logging.

capaths

Contains the authentication paths used with direct (nonhierarchical)
cross-realm authentication. Entries in this section are used by the
client to determine the intermediate realms which may be used in
cross-realm authentication. It is also used by the end-service when
checking the transited field for trusted intermediate realms.

If you are not using DNS TXT records, you must specify the
default_realm in the libdefaults section. If you are not
using DNS SRV records, you must include the kdc tag for each
realm in the realms section. To communicate with the kadmin
server in each realm, the admin_server tag must be set in the
realms section. If your domain name and realm name are not the
same, you must provide a translation in domain_realm. It is
also higly recommeneded that you create a [logging] stanza if
the computer will be functioning as a KDC so that the KDC and kadmind
will generate logging output.

4.1.1.3 kdc.conf

The kdc.conf file contains KDC configuration information,
including defaults used when issuing Kerberos tickets. Normally, you
should install your kdc.conf file in the directory
/usr/local/var/krb5kdc. You can override the default
location by setting the environment variable KRB5_KDC_PROFILE.

The kdc.conf file is set up in the same format as the
krb5.conf file. (See krb5.conf.) The kdc.conf file
may contain any or all of the following three sections:

kdcdefaults

Contains default values for overall behavior of the KDC.

realms

Contains subsections keyed by Kerberos realm names. Each subsection
describes realm-specific information, including where to find the
Kerberos servers for that realm.

logging

Contains relations which determine how Kerberos programs are to perform
logging.

4.1.1.4 Create the Database

You will use the kdb5_util command on the Master KDC to
create the Kerberos database and the optional stash file. The
stash file is a local copy of the master key that resides in
encrypted form on the KDC's local disk. The stash file is used to
authenticate the KDC to itself automatically before starting the
kadmind and krb5kdc daemons (e.g., as part of the
machine's boot sequence). The stash file, like the keytab file
(see See The Keytab File, for more information) is a potential
point-of-entry for a break-in,
and if compromised, would allow unrestricted access to the Kerberos
database. If you choose to install a stash file, it should be readable
only by root, and should exist only on the KDC's local disk. The file
should not be part of any backup of the machine, unless access to the
backup data is secured as tightly as access to the master password
itself.

If you choose not to install a stash file, the KDC will prompt you for
the master key each time it starts up. This means that the KDC will
not be able to start automatically, such as after a system reboot.

Note that kdb5_util will prompt you for the master key for the
Kerberos database. This key can be any string. A good key is one you
can remember, but that no one else can guess. Examples of bad keys are
words that can be found in a dictionary, any common or popular name,
especially a famous person (or cartoon character), your username in any
form (e.g., forward, backward, repeated twice, etc.), and any of
the sample keys that appear in this manual. One example of a key which
might be good if it did not appear in this manual is “MITiys4K5!”,
which represents the sentence “MIT is your source for Kerberos 5!”
(It's the first letter of each word, substituting the numeral “4” for
the word “for”, and includes the punctuation mark at the end.)

The following is an example of how to create a Kerberos database and
stash file on the master KDC, using the kdb5_util command. (The
line that begins with => is a continuation of the previous line.)
Replace ATHENA.MIT.EDU with the name of your Kerberos realm.

shell% /usr/local/sbin/kdb5_util create -r ATHENA.MIT.EDU -s
Initializing database '/usr/local/var/krb5kdc/principal' for
=> realm 'ATHENA.MIT.EDU',
master key name 'K/M@ATHENA.MIT.EDU'
You will be prompted for the database Master Password.
It is important that you NOT FORGET this password.Enter KDC database master key:<= Type the master password.Re-enter KDC database master key to verify:<= Type it again.shell%

This will create five files in the directory specified in your
kdc.conf file: two Kerberos database files, principal.db,
and principal.ok; the Kerberos administrative database file,
principal.kadm5; the administrative database lock file,
principal.kadm5.lock; and the stash file, .k5stash. (The
default directory is /usr/local/var/krb5kdc.) If you do not
want a stash file, run the above command without the -s option.

4.1.1.5 Add Administrators to the Acl File

Next, you need create an Access Control List (acl) file, and put the
Kerberos principal of at least one of the administrators into it. This
file is used by the kadmind daemon to control which principals
may view and make privileged modifications to the Kerberos database
files. The filename should match the value you have set for
“acl_file” in your kdc.conf file. The default file name is
/usr/local/var/krb5kdc/kadm5.acl.

The format of the file is:

Kerberos_principal permissions [target_principal] [restrictions]

The Kerberos principal (and optional target principal) can include the
“*” wildcard, so if you want any principal with the instance
“admin” to have full permissions on the database, you could use the
principal “*/admin@REALM” where “REALM” is your Kerberos
realm. target_principal can also include backreferences to
Kerberos_principal, in which "*number" matches the
component number in the Kerberos_principal.

Note: a common use of an admin instance is so you can grant
separate permissions (such as administrator access to the Kerberos
database) to a separate Kerberos principal. For example, the user
joeadmin might have a principal for his administrative
use, called joeadmin/admin. This way,
joeadmin would obtain joeadmin/admin
tickets only when he actually needs to use those permissions.

The permissions are represented by single letters; UPPER-CASE letters
represent negative permissions. The permissions are:

a

allows the addition of principals or policies in the database.

A

disallows the addition of principals or policies in the database.

d

allows the deletion of principals or policies in the database.

D

disallows the deletion of principals or policies in the database.

m

allows the modification of principals or policies in the database.

M

disallows the modification of principals or policies in the database.

c

allows the changing of passwords for principals in the database.

C

disallows the changing of passwords for principals in the database.

i

allows inquiries to the database.

I

disallows inquiries to the database.

l

allows the listing of principals or policies in the database.

L

disallows the listing of principals or policies in the database.

s

allows the explicit setting of the key for a principal

S

disallows the explicit setting of the key for a principal

*

All privileges (admcil).

x

All privileges (admcil); identical to “*”.

The restrictions are a string of flags. Allowed restrictions are:

[+ -]flagname

flag is forced to indicated value. The permissible flags are the same
as the + and - flags for the kadmin addprinc and
modprinc commands.

-clearpolicy

policy is forced to clear

-policy pol

policy is forced to be pol

expire time

pwexpire time

maxlife time

maxrenewlife time

associated value will be forced to MIN(time, requested value)

The above flags act as restrictions on any add or modify operation
which is allowed due to that ACL line.

Here is an example of a kadm5.acl file. Note that order is
important; permissions are determined by the first matching entry.

In the above file, any principal in the
ATHENA.MIT.EDU realm with an admin instance has all
administrative privileges. The user joeadmin
has all permissions with his admin instance,
joeadmin/admin@ATHENA.MIT.EDU (matches the first
line). He has no permissions at all with his null instance,
joeadmin@ATHENA.MIT.EDU (matches the second line).
His root instance has inquire and list permissions with any
other principal that has the instance root. Any principal
in ATHENA.MIT.EDU can inquire, list, or change the password of
their admin instance, but not any other admin instance.
Any principal in the realm ATHENA.MIT.EDU (except for
joeadmin@ATHENA.MIT.EDU, as mentioned above) has
inquire privileges. Finally, any principal with an admin instance
in EXAMPLE.COM has all permissions, but any principal that they
create or modify will not be able to get postdateable tickets or tickets
with a life of longer than 9 hours.

4.1.1.6 Add Administrators to the Kerberos Database

Next you need to add administrative principals to the Kerberos database.
(You must add at least one now.) To do this, use kadmin.localon the master KDC. The administrative principals you create
should be the ones you added to the ACL file. (See See Add Administrators to the Acl File.) In the following example, the
administration principal admin/admin is created:

4.1.1.7 Create a kadmind Keytab (optional)

The kadmind keytab is the key that the legacy admininstration daemons
kadmind4 and v5passwdd will use to decrypt
administrators' or clients' Kerberos tickets to determine whether or
not they should have access to the database. You need to create the
kadmin keytab with entries for the principals kadmin/admin and
kadmin/changepw. (These principals are placed in the Kerberos
database automatically when you create it.) To create the kadmin
keytab, run kadmin.local and use the ktadd command, as
in the following example. (The line beginning with => is a
continuation of the previous line.):

4.1.1.8 Start the Kerberos Daemons on the Master KDC

At this point, you are ready to start the Kerberos daemons on the Master
KDC. To do so, type:

shell% /usr/local/sbin/krb5kdc
shell% /usr/local/sbin/kadmind

Each daemon will fork and run in the background. Assuming you want
these daemons to start up automatically at boot time, you can add them
to the KDC's /etc/rc or /etc/inittab file. You need to
have a stash file in order to do this.

You can verify that they started properly by checking for their startup
messages in the logging locations you defined in /etc/krb5.conf.
(See Edit the Configuration Files.) For example:

4.1.2 Install the Slave KDCs

You are now ready to start configuring the slave KDCs. Assuming you are
setting the KDCs up so that you can easily switch the master KDC with
one of the slaves, you should perform each of these steps on the master
KDC as well as the slave KDCs, unless these instructions specify
otherwise.

4.1.2.1 Create Host Keys for the Slave KDCs

Each KDC needs a host principal in the Kerberos database. You can enter
these from any host, once the kadmind daemon is running. For
example, if your master KDC were called
kerberos.mit.edu, and you had two KDC slaves
named kerberos-1.mit.edu and
kerberos-2.mit.edu, you would type the following:

4.1.2.2 Extract Host Keytabs for the KDCs

Each KDC (including the master) needs a keytab to decrypt tickets.
Ideally, you should extract each keytab locally on its own KDC. If this
is not feasible, you should use an encrypted session to send them across
the network. To extract a keytab on a KDC called
kerberos.mit.edu, you would execute the following
command:

4.1.2.3 Set Up the Slave KDCs for Database Propagation

The database is propagated from the master KDC to the slave KDCs via the
kpropd daemon. To set up propagation, create a file on each KDC,
named /usr/local/var/krb5kdc/kpropd.acl, containing the
principals for each of the KDCs.
For example, if the master KDC were
kerberos.mit.edu, the slave KDCs were
kerberos-1.mit.edu and
kerberos-2.mit.edu, and the realm were
ATHENA.MIT.EDU, then the file's contents would be:

You will need a script to dump and propagate the database. The
following is an example of a bourne shell script that will do this.
(Note that the line that begins with => is a continuation of the
previous line. Remember that you need to replace /usr/local with
the name of the directory in which you installed Kerberos V5.)

As mentioned above, the stash file is necessary for your KDCs to be able
authenticate to themselves, such as when they reboot. You could run
your KDCs without stash files, but you would then need to type in the
Kerberos database master key by hand every time you start a KDC daemon.

4.1.5 Add Kerberos Principals to the Database

Once your KDCs are set up and running, you are ready to use
kadmin to load principals for your users, hosts, and other
services into the Kerberos database. This procedure is described fully in the
“Adding or Modifying Principals” section of the Kerberos V5 System
Administrator's Guide. (See Create Host Keys for the Slave KDCs, for a
brief description.) The keytab is generated by running kadmin
and issuing the ktadd command.

4.1.6 Limit Access to the KDCs

To limit the possibility that your Kerberos database could be
compromised, MIT recommends that each KDC be a dedicated
host, with limited access. If your KDC is also a file server, FTP
server, Web server, or even just a client machine, someone who obtained
root access through a security hole in any of those areas could gain
access to the Kerberos database.

MIT recommends that your KDCs use the following
/etc/inetd.conf file. (Note: each line beginning with =>
is a continuation of the previous line.):

4.1.7 Switching Master and Slave KDCs

You may occasionally want to use one of your slave KDCs as the master.
This might happen if you are upgrading the master KDC, or if your master
KDC has a disk crash.

Assuming you have configured all of your KDCs to be able to function as
either the master KDC or a slave KDC (as this document recommends), all
you need to do to make the changeover is:

If the master KDC is still running, do the following on the old
master KDC:

Kill the kadmind process.

Disable the cron job that propagates the database.

Run your database propagation script manually, to ensure that the slaves
all have the latest copy of the database. (See Propagate the Database to Each Slave KDC.) If there is a need to preserve per-principal
policy information from the database, you should do a “kdb5_util dump
-ov” in order to preserve that information and propogate that dump file
securely by some means to the slave so that its database has the correct
state of the per-principal policy information.

4.2.1 Client Programs

The Kerberized client programs are login.krb5, rlogin,
telnet, ftp, rcp, rsh, kinit,
klist, kdestroy, kpasswd, ksu, and
krb524init. All of these programs are in the directory
/usr/local/bin, except for login.krb5 which is in
/usr/local/sbin.

You will probably want to have your users put /usr/local/bin
ahead of /bin and /usr/bin in their paths, so they will by
default get the Kerberos V5 versions of rlogin,
telnet, ftp, rcp, and rsh.

MIT recommends that you use login.krb5 in place of
/bin/login to give your users a single-sign-on system. You will
need to make sure your users know to use their Kerberos passwords when
they log in.

You will also need to educate your users to use the ticket management
programs kinit,
klist, kdestroy, and to use the Kerberos programs
ksu, and kpasswd in place of their non-Kerberos
counterparts
su, passwd, and rdist.

4.2.2 Client Machine Configuration Files

Each machine running Kerberos must have a /etc/krb5.conf file.
(See krb5.conf.)

Also, for most UNIX systems, you must add the appropriate Kerberos
services to each client machine's /etc/services file. If you are
using the default configuration for Kerberos V5, you should be able
to just insert the following code:

As described in the comments in the above code, if your master
KDC or any of your slave KDCs is running Kerberos V4, (or if you will be
authenticating to any Kerberos V4 KDCs in another realm) you will need
to switch the port number for kerberos to 750 and create a
kerberos-sec service (tcp and udp) on port 88, so the Kerberos
V4 KDC(s) will continue to work properly.

4.2.2.1 Mac OS X Configuration

Mac OS X and Mac OS X Server use a database called NetInfo to store
the contents of files normally found in /etc. Instead of
modifying /etc/services, you should run the following commands
to add the Kerberos service entries to NetInfo:

In addition to adding services to NetInfo, you must also modify the
resolver configuration in NetInfo so that the machine resolves its own
hostname as a FQDN (fully qualified domain name). By default, Mac OS X
and Mac OS X Server machines query NetInfo to resolve hostnames before
falling back to DNS. Because NetInfo has an unqualified name for all
the machines in the NetInfo database, the machine's own hostname will
resolve to an unqualified name. Kerberos needs a FQDN to look up keys
in the machine's keytab file.

Fortunately, you can change the lookupd caching order to query
DNS first. Run the following NetInfo commands and reboot the machine:

4.3 UNIX Application Servers

An application server is a host that provides one or more services over
the network. Application servers can be “secure” or “insecure.” A
“secure” host is set up to require authentication from every client
connecting to it. An “insecure” host will still provide Kerberos
authentication, but will also allow unauthenticated clients to connect.

If you have Kerberos V5 installed on all of your client machines,
MIT recommends that you make your hosts secure, to take
advantage of the security that Kerberos authentication affords.
However, if you have some clients that do not have Kerberos V5
installed, you can run an insecure server, and still take advantage of
Kerberos V5's single sign-on capability.

4.3.1 Server Programs

Just as Kerberos V5 provided its own Kerberos-enhanced versions of
client UNIX network programs, Kerberos V5 also provides
Kerberos-enhanced versions of server UNIX network daemons. These are
ftpd, klogind, kshd, and telnetd.
These programs are installed in the directory
/usr/local/sbin. You may want to add this directory to
root's path.

4.3.3 The Keytab File

All Kerberos server machines need a keytab file, called
/etc/krb5.keytab, to authenticate to the KDC. The keytab file is
an encrypted, local, on-disk copy of the host's key. The keytab file,
like the stash file (Create the Database) is a potential
point-of-entry for a break-in, and if compromised, would allow
unrestricted access to its host. The keytab file should be readable
only by root, and should exist only on the machine's local disk. The
file should not be part of any backup of the machine, unless access to
the backup data is secured as tightly as access to the machine's root
password itself.

In order to generate a keytab for a host, the host must have a principal
in the Kerberos database. The procedure for adding hosts to the
database is described fully in the “Adding or Modifying Principals”
section of the Kerberos V5 System Administrator's Guide.
See Create Host Keys for the Slave KDCs. for a brief description.)
The keytab is generated by running kadmin and issuing the
ktadd command.

For example, to generate a keytab file to allow the host
trillium.mit.edu to authenticate for the services
host, ftp, and pop, the administrator
joeadmin would issue the command (on
trillium.mit.edu):

If you generate the keytab file on another host, you need to get a copy
of the keytab file onto the destination host (trillium, in the
above example) without sending it unencrypted over the network. If you
have installed the Kerberos V5 client programs, you can use
encrypted rcp.

4.3.4 Some Advice about Secure Hosts

Kerberos V5 can protect your host from certain types of break-ins,
but it is possible to install Kerberos V5 and still leave your host
vulnerable to attack. Obviously an installation guide is not the place
to try to include an exhaustive list of countermeasures for every
possible attack, but it is worth noting some of the larger holes and how
to close them.

As stated earlier in this section, MIT recommends that on a
secure host, you disable the standard ftp, login,
telnet, shell, and exec services in
/etc/inetd.conf. We also recommend that secure hosts have an empty
/etc/hosts.equiv file and that there not be a .rhosts file
in root's home directory. You can grant Kerberos-authenticated
root access to specific Kerberos principals by placing those principals
in the file .k5login in root's home directory.

We recommend that backups of secure machines exclude the keytab file
(/etc/krb5.keytab). If this is not possible, the backups should
at least be done locally, rather than over a network, and the backup
tapes should be physically secured.

Finally, the keytab file and any programs run by root, including the
Kerberos V5 binaries, should be kept on local disk. The keytab file
should be readable only by root.

5 Upgrading Existing Kerberos V5 Installations

If you already have an existing Kerberos database that you created with
a prior release of Kerberos 5, you can upgrade it to work with the
current release with the kdb5_util command. It is only
necessary to perform this dump/undump procedure if you were running a
krb5-1.0.x KDC and are migrating to a krb5-1.1.x or newer KDC or if you
were running a krb5-1.1.x KDC and are migrating to a krb5-1.2.x or newer
KDC. The process for upgrading a Master KDC involves the following
steps:

Create a new Master KDC installation (See Install the Master KDC.). If you have a stash file for your current database, choose any
new master password but then copy your existing stash file to the
location specified by your kdc.conf; if you do not have a stash file for
your current database, you must choose the same master password.

Load your old Kerberos database into the new system with
kdb5_util's “load” command:

The “dump -ov” and “load -update” commands are necessary in order to
preserve per-principal policy information, since the default dump format
filters out that information. If you omit those steps, the loaded
database database will lose the policy information for each principal
that has a policy.

To update a Slave KDC, you must stop the old server processes on the
Slave KDC, install the new server binaries, reload the most recent slave
dump file, and re-start the server processes.

5.1 Upgrading to Triple-DES Encryption Keys

Beginning with the 1.2 release from MIT, Kerberos includes
a stronger encryption algorithm called “triple DES” – essentially,
three applications of the basic DES encryption algorithm, greatly
increasing the resistance to a brute-force search for the key by an
attacker. This algorithm is more secure, but encryption is much
slower.

Release 1.1 had some support for triple-DES service keys, but with
release 1.2 we have added support for user keys and session keys as
well. Release 1.0 had very little support for multiple cryptosystems,
and some of that software may not function properly in an environment
using triple-DES as well as plain DES.

In the 1.3 release from MIT, Kerberos also includes the RC4
encryption alogorithm, a stream cipher symmetric key algorithm
developed in 1987 by Ronald Rivest at RSA Data Security. Please note
that RC4 is not part of the IETF standard.

Because of the way the MIT Kerberos database is structured, the KDC
will assume that a service supports only those encryption types for
which keys are found in the database. Thus, if a service has only a
single-DES key in the database, the KDC will not issue tickets for that
service that use triple-DES or RC4 session keys; it will instead issue
only single-DES session keys, even if other services are already
capable of using triple-DES or RC4. So if you make sure your
application server software is updated before adding a triple-DES or
RC4 key for the service, clients should be able to talk to services at
all times during the updating process.

Normally, the listed supported_enctypes in kdc.conf are
all used when a new key is generated. You can control this with
command-line flags to kadmin and kadmin.local. You may
want to exclude triple-DES and RC4 by default until you have updated a
lot of your application servers, and then change the default to include
triple-DES and RC4. We recommend that you always include
des-cbc-crc in the default list.

6 Bug Reports for Kerberos V5

In any complex software, there will be bugs. If you have successfully
built and installed Kerberos V5, please use the krb5-send-pr
program to fill out a Problem Report should you encounter any errors in
our software.

Bug reports that include proposed fixes are especially welcome. If you
do include fixes, please send them using either context diffs or unified
diffs (using diff -c or diff -u, respectively). Please be
careful when using “cut and paste” or other such means to copy a patch
into a bug report; depending on the system being used, that can result
in converting TAB characters into spaces, which makes applying the
patches more difficult.

The krb5-send-pr program is installed in the directory
/usr/local/sbin.

The krb5-send-pr program enters the problem report into our
Problem Report Management System (PRMS), which automatically assigns it
to the engineer best able to help you with problems in the assigned
category.

The krb5-send-pr program will try to intelligently fill in as
many fields as it can. You need to choose the category,
class, severity, and priority of the problem, as well
as giving us as much information as you can about its exact nature.

Choose the category that best describes the area under which your
problem falls.

The class can be sw-bug, doc-bug, change-request,
or support. The first two are exactly as their names imply. Use
change-request when the software is behaving according to
specifications, but you want to request changes in some feature or
behavior. The support class is intended for more general questions
about building or using Kerberos V5.

The severity of the problem indicates the problem's impact on the
usability of Kerberos V5. If a problem is critical, that
means the product, component or concept is completely non-operational,
or some essential functionality is missing, and no workaround is known.
A serious problem is one in which the product, component or
concept is not working properly or significant functionality is missing.
Problems that would otherwise be considered critical are rated
serious when a workaround is known. A non-critical problem is
one that is indeed a problem, but one that is having a minimal effect on
your ability to use Kerberos V5. E.g., The product, component
or concept is working in general, but lacks features, has irritating
behavior, does something wrong, or doesn't match its documentation. The
default severity is serious.

The priority indicates how urgent this particular problem is in
relation to your work. Note that low priority does not imply low
importance.
A priority of high means a solution is needed as soon as possible.
A priority of medium means the problem should be solved no later
than the next release. A priority of low means the problem should
be solved in a future release, but it is not important to your work how
soon this happens. The default priority is medium.

Note that a given severity does not necessarily imply a given priority.
For example, a non-critical problem might still have a high priority if
you are faced with a hard deadline. Conversely, a serious problem might
have a low priority if the feature it is disabling is one that you do
not need.

It is important that you fill in the release field and tell us
what changes you have made, if any.

A sample filled-out form from a company named “Toasters, Inc.” might
look like this:

If the krb5-send-pr program does not work for you, or if you did
not get far enough in the process to have an installed and working
krb5-send-pr, you can generate your own form, using the above as
an example.

Footnotes

[1] Kerberos V4 used port 750. If
necessary, you can run on both ports for backward compatibility.

[2] If you are fortunate enough to
have a previous version of Kerberos V5 or V4 installed, and the Kerberos
rlogin is first in your path, you can setup .k5login or
.klogin respectively to allow you access.